As a next-generation energy source, various fuel cell apparatuses generating power using hydrogen-containing gas and oxygen-containing gas have been proposed.
In general, such fuel cell apparatuses are configured to receive a fuel cell device, in which plurality of fuel cells are combined, in a housing and generate power by supplying fuel gas (hydrogen-containing gas) to a fuel electrode layer of each fuel cell and supplying air (oxygen-containing gas) to an air electrode layer. The plurality of fuel cells are electrically connected in series to each other with a felt-like or plate-like collector member interposed therebetween. Such a collector member is generally formed of a composite body with high workability and heat resistance and is formed of, for example, a Cr-containing alloy.
However, when the collector member is formed of the Cr-containing alloy, diffusion of Cr (hereinafter, also referred to as “Cr diffusion”) from the alloy may be caused at the time of operating the fuel cell apparatus and there is thus a problem in that the heat resistance of the alloy decreases with the decrease in the amount of Cr contained in the alloy.
Therefore, in order to reduce the Cr diffusion, the use of a composite body in which the surface of the Cr-containing alloy is coated with a metal oxide film of Mn, Fe, Co, Ni, or the like has been proposed (see Patent Literature 1).
The use of a composite body in which a coating layer having a first layer containing Zn and a second layer, which is disposed on the first layer, containing ZnO and a metal element of which the valence is +3 or higher is provided to the surface of a Cr-containing alloy has been also proposed (see Patent Literature 2).